What distinguishes a shaman from a priest?

What distinguishes a shaman from a priest?
 
  A) Priests, but not shamans, have the ability to work magic in religious rituals and cause ritual items to change their substance.
  B) Shamans are part-time practitioners who mediate the worlds of the natural and supernatural. Priests are formally elected or appointed as full-time religious officers.
  C) Priests have training and undergo an apprenticeship in order to serve a group of people. Shamans are untrained because they are thought to have a natural affinity to the supernatural.
  D) Shamans are found in state societies and priests are found in foraging and egalitarian societies.
  E) There are no differences between shamans and priests. Priests are classified as a type of shaman.